Effects of phytoecdysone on the molting period and survival rate of the blue swimming crab, Portunus pelagicus.

Abstract

ABSTRACT           To develop synchronized molting for soft-shell crab production, phytoecdysone, a plant steroid, is used as a stimulant instead of cutting eyestalks or limbs. Therefore, a study was performed to examine the effects of phytoecdysteroid extracts from Vitex glabrata on molting period and survival rate of the blue swimming crab, Portunus pelagicus. Post-molt (B) stage, inter-molt (C2) stage, pre-molts (D1 and D2) stages were, respectively, injected with a single dose of phytoecdysone at 0.1, 0.2, 0.3, 0.4, 0.5, and 1.0 µg/g body weight. The results showed that the effective doses significantly shortening molting periods were 0.4 µg/g BW, 0.5 µg/g BW, and 0.1, 0.4 µg/g BW when injections were performed on stages B, C2, and D1, respectively. However it could not induce molting by this method at stage D2, and molting was inhibited by the injection. An injection at stage B, survival rate of crabshowed significantly higher than those of control at 0.1, 0.2, and 1.0 µg/g BW. As well, the survival rate of treatments showed significantly higher than those of control for injection at stage C2. In contrast, injection at stage D1, survival rates of 0.1, 0.2, and 1.0 µg/g BW were not significantly different from control, but were significantly lower than those of control at doses of 0.3, 0.4, and 0.5 µg/g BW. Survival rate was significantly different between control and treatments at injection of stage D2. The results indicated that, except for D2, the effective dosages for reducing the molting period injection at stage B, C2, and D1 were 0.4, 0.5, and 0.1 µg/g BW, respectively.